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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 0 |
| 2 | 4 |
| 3 | 16 |
| 4 | 80 |
| 5 | 384 |
| 6 | 1856 |
| 7 | 8960 |
| 8 | 43264 |
| 9 | 208896 |
| 10 | 1008640 |
| 11 | 4870144 |
| 12 | 23515136 |
| 13 | 113541120 |
| 14 | 548225024 |
| 15 | 2647064576 |
| 16 | 12781158400 |
| 17 | 61712891904 |
| 18 | 297976201216 |
| 19 | 1438756372480 |
| 20 | 6946930294784 |
| 21 | 33542746669056 |
| 22 | 161958707855360 |
[1,0,4,16,80,384,1856,8960,43264,208896,1008640, 4870144,23515136,113541120,548225024,2647064576, 12781158400,61712891904,297976201216, 1438756372480,6946930294784,33542746669056, 161958707855360] |